问题 单项选择题

以下关于卞索引和候选索引的叙述正确的是( )。

A. 主索引和候选索引都能保证表记录的惟一性

B. 主索引和候选索引都可以建立在数据库表和自由表上

C. 主索引可以保证表记录的惟一性,而候选索引不能

D. 主索引和候选索引是相同的概念

答案

参考答案:A

解析:主索引和候选索引都要求了字段值的惟一,不允许出现重复的记录。但由于主索引中不允许出现重复值,一个表 只能有一个主关键字,因此一个表只能建立一个主索引,建立候选索引的字段可以看做是候选关键字,它也要求 的字段值的唯一性,但可以建立多个。

阅读理解

When I was young, my father used to grow carnations — a kind of flower that was red, pink or white. He took care of them with much love and devotion. Every day he came home from work, he would enjoy watching them. And he used to tell us, “No one should touch my flowers.”

One day, my younger sister Clemence, who loved dad very much, wanted to help him. So she cut the carnation from their stems(枝干)one by one and arranged them on the ground. She believed that dad would be very pleased to see them that way.

When mom and I realized what my sister had done, we became completely speechless. However, my sister had no idea why no one showed her any appreciation. When dad arrived, he went as usual straight to watch the flowers. Seeing his flowers lying on the ground like dead animals, he was shocked at first. He looked towards the street to see if it was any of the neighbors’ children who could have done it. Then he looked at mom in silence. Finally mom, who always taught us to tell the truth no matter what, said, “No bad neighbors did this great job, only your lovely daughter Clemence.”

Dad’s face changed into a smile and then he said, “Do I have better flower than my lovely daughter?” My younger sister smiled and hugged(拥抱)dad strongly.

小题1:How did Clemence feel when she had the carnations cut?

A.Lucky.

B.Helpful.

C.Upset.

D.Worried.小题2:Which of the following is TRUE according to the passage?

A.No one knew what my sister had done with the carnations.

B.My younger sister told my father the truth about the carnations.

C.Dad had thought one outsider had cut the flowers from the stems.

D.Dad asked my sister to help arrange the carnations on the ground.小题3:What caused my younger sister to smile and hug dad strongly?

A.Mom’s help.

B.Mom’s words.

C.Dad’s silence.

D.Dad’s love.小题4:Which of the following would be the best title for the passage?

A.My Neighbors

B.Telling the truth

C.Growing Carnations

D.Dad’s Best Flower

单项选择题 案例分析题